Cordierite ceramics are useful in systems where rapid temperature changes take place because crystalline cordierite has a very low thermal expansion. In particular, cordierite may be successfully used as a catalyst support in many catalytic systems including the automobile pollution control catalytic converter.
Unfortunately, cordierite has a fairly low melting point and is not useful for even short periods at temperatures greater than about 1500.degree. C. because of melting and resulting physical deformation. Other ceramic materials which are more refractory than cordierite and would have higher prolonged use temperatures (e.g. alumina), unfortunately have much higher expansions (alumina about 88 .times. 10.sup.-7 in/in/.degree. C.), and are more adversely affected by a thermal shock. For example, in an automobile exhaust system, temperatures may rise very quickly to very high temperatures for short periods of time during start up and then drop and level off to operating temperatures of around 800.degree.-1000.degree. C. The thermal "spikes," as these short temperature excursions are named, can locally melt a low-expansion, moderately refractory material such as cordierite or can fracture a higher expansion, highly refractory material such as alumina or zirconia.